Prior to the present invention, various techniques were developed for eliminating PCBs, or polychlorinated biphenyls from the environment. In instances where the PCBs were dissolved in an organic solvent, such as transformer oil, the contaminated solution could be treated with a mixture of polyethylene glycol and alkali metal hydroxide as shown by Brunelle, U.S. Pat. No. 4,351,718, assigned to the same assignee as the present invention and incorporated herein by reference. In many cases, the PCBs are located in more exposed environmental areas, such as landfill sites, river beds and sewage sludge. Direct chemical treatment of PCBs in such contaminated sites is often not feasible since the resulting treated solids are difficult to process further and recycle.
As shown by Colaruotolo et al., U.S. Pat. No. 4,447,570, an alternate procedure can be used for treating halogenated organic waste by effecting the removal of halogenated aromatics from the contaminated organic waste by microbial degradation. As taught by Colaruotolo et al., microorganisms have been identified having the capability of efficiently utilizing various aromatic organic chemicals as carbon sources for growth. In addition, microorganisms also have been isolated from the environment that are capable of growing in the presence of chlorinated aromatic compounds. Experience has shown, however, that PCBs found in weathered environmental soil samples, often contain five or more chemically combined chlorine atoms per molecule, indicating that such polychlorinated biphenyls generally resist biodegradation.
It has been further found that not only does the total number of chemically combined chlorine atoms per biphenyl nucleus influence the manner by which PCBs resist biodegradation, but the location of chlorine atoms substitution on the biphenyl nucleus is also an important factor. For example, the positions of chlorine substitution on a biphenyl nucleus is shown as follows: ##STR1##
It has been found that PCB congeners having all 2,3 positions blocked by chlorine atoms often require a 3,4-dioxygenase, while those having all 3,4 positions blocked often require a 2,3-dioxygenase for aerobic bacterial degradation. Theoretically, PCBs having no vicinal unchlorinated carbon atoms would not be degradable by a dioxygenase.
It would be desirable, therefore, to provide aerobic bacteria capable of degrading a broad spectrum of PCBs having more than five chlorine atoms per biphenyl nucleus, including those having either 2,3 positions blocked, 3,4 positions blocked, those having all of these positions blocked, or no 2,3 or 3,4 positions available, or PCB congeners having no vicinal unchlorinated carbon atoms.
The present invention is based on the discovery that a particular strain of Pseudomonas, having the identifying characteristics of Pseudomonas putida NRRL B-18064 can be used to degrade PCB congeners having no vicinal unchlorinated carbon atoms, having only 2,3 positions unchlorinated, having only 3,4 positions unchlorinated, and having both 2,3 and 3,4 positions unchlorinated. The aforementioned Pseudomonas strain, or "LB400", was isolated from a soil sample contaminated with Aroclor 1242 and obtained from a dump site. Another unexpected feature of the present invention is the enrichment procedure employed leading to the selection of LB400, utilizing as a sole carbon source, a mixture of biphenyl and monochlorobiphenyl-containing PCB having an average of at least about 15% of chemically combined chlorine by weight. In addition, LB400 has been found to provide metabolites comprising 3,4- and 2,3-dihydroxybiphenyls and epoxy-substituted biphenyls.